1. Field of the Invention
The field of the invention relates to life safety systems generally, and more particularly to certain new and useful advances in detecting an alarm condition and propagating a failsafe alarm signal under catastrophic failure conditions within a life safety system itself, of which the following is a specification, reference being had to the drawings accompanying and forming a part of the same.
2. Discussion of Related Art
Life safety systems, including fire detection systems and mass notification systems, include many components, such as fire notification devices, mass notification devices, network adapters, amplifiers, and the like, each of which may include firmware and/or one or more microprocessors. Without backup or other failsafe designs, a catastrophic failure within a life safety system can put lives at risk. Examples of a catastrophic failure include, but are not limited to, at least an inoperable microprocessor, defective firmware, and the like.
A common approach to protecting a microprocessor-based life safety system against catastrophic system failure is to include one or more redundant microprocessors and one or more redundant memory components in the microprocessor-based life safety system. This approach, though effective, is a relatively complex and expensive solution; and the increased system complexity sometimes actually reduces the reliability of the microprocessor-based life safety system. Moreover, this approach does not properly address catastrophic failures caused by defective firmware. For example, with the primary microprocessor and its redundant microprocessor each running the same application firmware, there is little reason to expect that the redundant microprocessor would produce a different result when faced with the same firmware defect(s) as the primary microprocessor. FIG. 3 is a high level block diagram of a conventional primary processor 301, which includes a core microprocessor 304 coupled with a power conditioner 302, a nonvolatile (flash) memory 305, a clock 303, and a volatile (ram) memory 306.
Less complex failsafe mechanisms than redundant microprocessors and redundant memories have existed previously, but knowledge and teachings in the art have heretofore restricted their scope of application to a single node on a network. The term “network node” is defined below. Examples of such less complex failsafe mechanisms include EST3 and IRC3 life safety systems. Although effective at minimizing a node's chances of experiencing catastrophic failure, these less complex failsafe mechanisms do not adequately address how to propagate alarms though a life safety system when one or more network nodes distributed across the life safety system become inoperable or operate in a defective manner.
What is needed is a relatively simple and inexpensive safeguard that permits a life safety system to continue functioning in the event of a catastrophic failure within the life safety system.